Chemoreception, regarded as vitally important for all animals, encompasses olfaction, pheromone detection, hormonal signaling and various other essential processes. Siimilar responses to chemical cues are shared in a phylogenetically broad array of animals, implying that there is an ancient solution to the problem of detecting and discriminating odorants, and what is learned in one system can be applied to others. The Daphnia genome has recently been sequenced and a set of 58 gustatory receptor genes (Grs) has been identified. 49 of these Grs are members of a Daphnia-specific clade (when compared to insects), with 2-3 Grs resembling known arthropod sugar receptors. This relatively small set of receptor genes is presumably the basis for much of Daphnia's behavioral repertoire. In particular, several Daphnia Grs appear to have sex-biased expression, not uncommon among organisms, and are candidates to mediate mating behavior. As D. pulex clones can exhibit both cyclical parthenogenesis (ie. sexual reproduction) and obligate asexuality, we can investigate the evolution of the Gr family in the context of sexual selection. The long term aim of this research is to establish a foundation for the molecular and evolutionary understanding of Chemoreception in a model crustacean, using bioinformatics, gene evolution theory, molecular techniques, and the newly sequenced genome of Daphnia. How chemical cues are detected in an aquatic system is not well understood, yet necessary to combat many known pests with aquatic larval stages, such as mosquito larvae. Such understanding may help us develop ways of interfering with their survival and development, thus decreasing the spread of diseases such as dengue and yellow fever. In addition, the health of our aquatic ecosystems relies heavily on the ability of its inhabitants, including zooplankton, to detect and eat algae and bacteria. When we interfere with their ability to detect critical chemical cues, through toxins or other anthropogenic chemicals, we in fact can cause toxic algal blooms, increase the occurrence of disease-carrying bacteria (such as Vibrio cholera), and destroy balanced ecosystems.